The invention relates to a coolant circuit having an engine cooling circuit and a transmission cooling circuit which branches off from the engine cooling circuit.
Modern high-performance transmissions, in particular dual-clutch transmissions, are also cooled with water in addition to oil cooling. In this instance, coolant is branched off from the engine cooling circuit and used to cool the transmission. However, it has been found with this type of cooling that over wide operating ranges the relatively warm coolant in the coolant circuit leads to the transmission being actually heated in certain operating ranges rather than cooled. Only in high power ranges is this effect reversed so that the transmission is cooled.
There is therefore a needed an improved cooling of liquid-cooled transmissions.
An object of the present invention is to provide a coolant circuit for cooling a transmission which has improved cooling properties. This object is achieved with a coolant circuit, a motor vehicle having the coolant circuit, and a control method of controlling the coolant circuit in accordance with embodiments of the invention.
According to an embodiment of the invention, a coolant circuit is provided having an engine cooling circuit in which coolant can be circulated in order to cool an internal combustion engine; having a transmission cooling circuit for cooling a transmission which branches off from the engine cooling circuit; having a valve which is arranged at least in the transmission cooling circuit, and having a control which is adapted to open and close the valve in accordance with an operating state of the internal combustion engine and/or the transmission. The operating state of the internal combustion engine may, for example, be determined by way of a throttle valve position, an engine speed and/or an engine torque. Furthermore, the control may be adapted to control (to open and close) the valve in accordance with at least one of the following parameters: a coolant temperature, a crank housing temperature.
As described in the introduction, it has been found that conventional coolant circuits at low engine power heat, rather than cool, the transmission. Furthermore, this also has a negative influence on the heating speed of the internal combustion engine in the warm-up phase, which may have an influence on emissions and fuel consumption. This is prevented by the provision of a possible method for switching off the transmission cooling circuit in accordance with the engine power. Since, at high engine power, the transmission can be cooled very effectively by the coolant, from a specific engine power from which the cooling action takes effect, a flow of coolant through the transmission cooling circuit is permitted.
According to another embodiment of the invention, the engine cooling circuit comprises a cylinder head cooling circuit and separately therefrom a crank housing cooling circuit, wherein the transmission cooling circuit branches off from the crank housing cooling circuit, that is to say, branches off at a portion along which the crank housing cooling circuit is separated from the cylinder head cooling circuit. The advantage which is afforded by this coolant switching is that, with so-called split cooling engines in which a separate crank housing and cylinder head cooling circuit is provided, the cylinder head cooling circuit has a permanent throughflow and it is sufficient for the crank housing cooling circuit to be flowed through only from a specific engine power. The inventor of this invention discovered that by coupling the transmission cooling circuit to the crank housing cooling circuit, an additional separate valve for the transmission cooling circuit can be saved since the crank housing and the transmission have similar cooling conditions and consequently a common valve for the transmission cooling circuit and the crank housing cooling circuit can be used. In this embodiment, the valve (the same valve) is consequently arranged in the transmission cooling circuit and in the crank housing cooling circuit, that is to say, the transmission cooling circuit and the crank housing circuit are identical at least at the input or at the output of the valve.
According to another embodiment of the invention, a coolant circuit is provided, wherein the crank housing cooling circuit has a crank housing water jacket which is guided around cylinder bores, and the transmission cooling circuit opens in the crank housing water jacket downstream of a device for absorbing heat from the transmission, in particular a water jacket in the transmission housing or a heat exchanger for heat transmission with the transmission oil. In particular, the valve is located downstream of the crank housing water jacket.
According to another embodiment of the invention, downstream of the valve the cylinder head cooling circuit and the crank housing cooling circuit are merged again.
According to another embodiment of the invention, the engine cooling circuit branches off at a branch into the cylinder head cooling circuit and the crank housing cooling circuit, wherein the transmission cooling circuit branches off downstream of the branch from the crank housing cooling circuit.
According to another embodiment of the invention, the transmission cooling circuit branches off from the crank housing cooling circuit downstream of the branch and upstream of a crank housing water jacket of the crank housing cooling circuit.
According to another embodiment of the invention, a coolant circuit is provided, wherein the crank housing cooling circuit branches off downstream of the branch into a crank housing water jacket and an engine oil cooling circuit which is adapted to cool an engine oil via a heat exchanger. The transmission cooling circuit branches off from the engine oil cooling circuit.
According to another embodiment of the invention, a non-return valve is provided in the transmission cooling circuit. This non-return valve is intended to prevent, in particular in the split cooling system, flow through the crank housing water jacket and in the reverse direction the transmission cooling circuit when the transmission cooling circuit valve is closed.
According to another embodiment of the invention, the branch is formed by a coolant pump.
According to another embodiment, the control is adapted to open and close the valve in accordance with an engine speed and/or an engine torque. Furthermore, the control may be adapted to control (open and close) the valve in accordance with at least one of the following parameters: a coolant temperature, a crank housing temperature.
According to another embodiment, the control is adapted to open the valve only above a specific threshold value of the engine speed and/or the engine torque. This means that the control is adapted to open the valve above the threshold value and to close the valve below the threshold value (including the threshold value itself). In particular, the control is adapted to completely open the valve above the threshold value and to completely close the valve below the threshold value (including the threshold value itself). The engine speed and the engine torque determine an engine power. In this instance, the control may be adapted to open the valve only above a threshold value of the engine power of 70% of the maximum engine power, the so-called nominal engine power. In particular the threshold value is 80%.
Furthermore, the invention relates to a vehicle having a coolant circuit according to one of the embodiments.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.